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NIVERSITY  OF  ILLINOIS  BULLETIN 

Vol.  VII.  MARCH  28,  1910.  No.  30 

[Entered  February  14,  1902,  at  Urbana,  Illinois,  as  second-class  matter  under 
Act  of  Congress  of  July  16,  1894.] 


BULLETIN  No.    15 
DEPARTMENT  OF  CERAMICS 

A.   V.   BLEININGER,  Director 

SOME  CHEMICAL  AND  PHYSICAL  CHANGES 

IN  CLAYS  DUE  TO  THE  INFLUENCE 

OF  HEAT 

BY 

J.   M.   KNOTE 

URBANA,   ILL. 


1909-1910 


PUBLISHED  FORTNIGHTLY  BY  THE  UNIVERSITY 


[Reprinted  from  Transactions  of  American  Ceramic  Society,  Vol.  XII. 
Paper  read  at  Pittsburgh  Meeting,  February,  1910] 


SOME    CHEMICAL    AND    PHYSICAL    CHANGES    IN 
CLAYS  DUE  TO  THE  INFLUENCE  OF  HEAT. 

BY 

J.  M.  Knotb,  Urbana,  111. 

All  who  have  studied  clays  are  aware  that  the  temper- 
ature range  in  which  chemical  and  physical  changes  may 
take  place,  extends  from  the  ordinary  atmospheric  temper- 
ature up  to  about  1850°C,  at  which  point  even  the  most 
refractory  clay  is  profoundly  affected,  both  by  physical 
and  chemical  reactions.  The  temperature  intervals  in 
which  reactions  of  commercial  importance  occur  have 
been  studied  with  more  or  less  thoroughness,  as  a  survey 
of  the  literature  will  show.  Ashley1,  in  his  studies  of  the 
colloidal  matter  in  clays,  worked  at  ordinary  atmospheric 
temperatures.  Bleininger2  heated  clays  to  a  point  consid- 
erably below  the  temperature  of  dehydration,  and  produced 
reactions  of  great  practical  importance.  The  dehydration 
of  clays  has  been  studied  by  numerous  workers.  F.  W. 
Clark3  and  others  have  attempted  to  determine  the  com- 
pounds formed  when  dehydration  occurs.  Le  Chatelier 
determined  the  heat  changes  in  some  clays  when  they  were 
heated  rapidly  from  atmospheric  temperatures  to  a  high 
heat.  Purdy4,  Bleininger5  and  others  have  studied  the 
physical  and  chemical  changes  produced  in  clays,  and  mix- 
tures of  flays  with  other  substances,  between  cone  010  and 
cone  11.  The  formation  of  sillimanite  at  about  1350°C 
has  been  the  subject  of  much  experimentation  and  specu- 
lation, and  finally  the  determination  of  the  point  of  fusion 
of  fire  clays  has  become  common. 

»  Trans.  A.  C.  S.,  Vol.  XI. 

2  Trans.  A.  C.  S.,  Vol.  XI. 

3  Bulletin  125.  U.   S.   Geological   Survey. 
*  Trans.  A.  C.  S.,  Vol.  IX. 

3  Trans.  A.  C.  S.,  Vol.  X. 

1 


2  CHEMICAL    AND    PHYSICAL    CHANGES   IN    CLAYS. 

It  is  apparent  that  very  little  attention  has  been  paid 
to  what  takes  place  in  a  clay  from  the  time  it  begins  to 
lose  its  combined  water  until  it  reaches  a  point  where  the 
reactions  of  vitrification  are  started.  And  there  has  been 
no  data  published  on  the  physical  and  chemical  behavior 
of  fire  clays  at  temperatures  above  cone  11  and  below  their 
fusing  point.  So  the  object  of  this  work  is  to  investigate1 
these  neglected  regions. 

The  work  naturally  divides  itself  into  two  parts:  one 
an  investigation  of  the  behavior  of  clays  below  1000°C,  and 
the  other  the  behavior  of  refractory  clays  above  1000°C. 

PART  I. 

INVESTIGATION  OF  THE  CHEMICAL  AND  PHYSICAL 
CHANGES  THAT  OCCUR  IN  CLAYS  AT  TEMPERA- 
TURES BELOW  1000°C. 

Method  of  Investigation. 

Above  cone  010,  changes  in  porosity  and  apparent 
specific  gravity  of  trial  pieces  indicate  chemical  and  phy- 
sical changes,  and  have  been  found  of  great  value  in  study- 
ing clays,  but  below  cone  010  these  methods  of  investiga- 
tion do  not  apply.  The  true  specific  gravity,  as  determined 
with  the  pyenometer,  and  the  chemical  properties  of  the 
material,  would  be  most  likely  to  indicate  and  explain  any 
changes  which  take  place. 

Determination  of  True  Specific  Gravity  of  High  Grade 
Clays  Heated  to  Temperatures  Below  1000°C. 

A  series  of  the  purer  clays  was  selected  to  include  plas- 
tic and  non-plastic  fire  clays,  ball  clays,  kaolins,  etc. 
Shales  and  red-burning  surface  clays  were  not  included, 
as  it  was  desired  to  avoid  as  far  as  possible  the  effect  of 
the  ordinary  diluting  minerals.  The  clays  were  pulverized 
to  pass  an  eighty  mesh  sieve.  Samples  were  put  into  por- 
celain crucibles  and  these  fired  in  the  laboratory  test  kiln 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


described  by  Purdy,  Vol.  IX,  Trans.  A.  C.  S.  The  tem- 
peratures were  determined  by  means  of  a  pyrometer,  the 
end  of  the  couple  being  placed  as  close  as  possible  to  the 
crucibles  to  be  drawn.  A  sample  of  each  clay  was  drawn 
at  intervals  of  100°C  up  to  a  temperature  of  450  C,  and 
after  that,  every  50°C  up  to  1000°C.  It  was  not  possible 
to  burn  all  the  clays  at  once,  but  eight  burns  were  neces- 
sary. 

The  specific  gravity  of  these  samples  was  determined 
by  means  of  the  pyenometer,  or  specific  gravity  bottle.  The 
methods  of  doing  this  are  described  in  various  text  books. 
Bleininger,  Vol.  XI,  Trans.  A.  C.  S.,  gives  the  details  of 
the  method  and  apparatus  used  in  the  Ceramic  Laboratory 
of  the  University  of  Illinois.  The  results  shown  in  Table 
No.  1,  and  Curves  1  and  2,  were  obtained  by  this  means. 

TABLE  No.   1. 
Pyenometer  Results   on  Various   High   Grade   Clays. 


V 

e  * 

> 

_■     > 

a 

o 

3      E 

5  u 
B.  ~ 

s  ij 

■—    M 
Q 

*5 

55  e 

.  5 

&  a 

_.  s, 
a  | 

=  ^ 

o 

.2  a 

n 

ft 

a 
"3  a 

P 

o 

Z 

X  s 

'■-      R 

°  E 

d 
Z  jf 

v  D 

e  ~ 

S 
- 

dS 

2h 

11 

c  o 

a    . 
o  o 
-'Z 

c  t 

1  » 

5  z 

1« 

—  d 

"3° 
0, 

o     « 

o    e 

*  5 

'JO 

O    co 

E    U 

c 

«    E 

:'    5 

Raw     .... 

2.60 

2.64 

2.60 

2.60 

2.6412.61 

2.64 

2.64 

1 

2. 64(2. 64l2. 59|2.64I2. 56 

450     

2.62|2.63 

2.59:2.56  2.64  2.61  2.6412.642.62  2.66[2.59  2.62  2.62 

500    

2.58  2.58 [2.55(2.55  2.51 

2.54 

2.54  2. 59|2. 6212.53(2. 61|2.55 

550    

2.4812.512.50  2.47  2.52  2.48 

2.50 

2.5312.56 

2.5712.4712.5812.47 

600 

2.49  2. 51[2. 4812.46(2. 5212. 51 
2.51  2.53  2.50  2.49  2.53  2.52 

! 

....I....I. ...'.... 

650     

700 

2.52  2. 5412. 5112. 511 

2    54  9.    ".n  9    K9!I9!    521 

2.52 

1 |. ... 

750    

800 

2  53 

::::l::::i:::::::: 

2  56 

■'   "t:  I  5312.54  2.55 

9        53 

.......  J....I.... 

850    

2.5? 

1 i.  ...12.52 

900    

2 .  59(2 .  59  2 .  55  2 .  59[2 .  59  2  .  55 

2.5612.55  2. 56!2. 5412. 5012. 51(2.52 

950    

2.70  2. 7012. 7012. 7212. 6612.66 

2. 59|2.61  |2.59I2. 6412. 52!2.64|2. 55 

1000    .... 

2.70|2.70|2.69|2.72|2.63'2.65 

1      1      !      1       1 

2. 6fi|2.66|2.  66'2.69I2. 6112. 6412. 57 

1         i         1         1         i 

CHEMICAL    AN'D    PHYSICAL    CHANGES    IN    CLAYS 


THArsis 

A  (VI 

CER 

SOC      VOL  XII 

<  NO 

TE 

2.7 

i 

> 

2.6 

-^ C 

2.5 

1 

0 
^2.3 

is 

Temperature  -  Specific  Gravity    Curve. 

Tennessee   A'oJ  Bali Clay. 

10 

2.1 

Raw  50      100     150    ZOO     250    300     350    4C0     450    500    550    600    650    700     750 
Te  m  ji  e  ret  t  ur-e        //?   lenrees    Ce/itiqi^cide 


35C    9K     S50    1053 


TRA? 

5.    A\ 

I    CE? 

SOC 

VOL 

(II. 

■;N  on 

E 

1 

z.ei 

>— J 

J 

2.5 

^ 

^5 
y  2.3 

Temperature-  6/iecific  Gravity  Curve. 

Olive  Hill,  Ky.  Clint  Tire  Clay. 

§&z. 

2.1 

Paw    5(1      100     150     ZOO    250     300     3S0    400    450     500     550     600    650    700    750    800    650    900    950    1000. 
Begrees    C ' entic/rade 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


ICOC 

SCO 


Vj   500 

^400 

300 

iOO 

100 


1 v,         ■ 

Time  -  Temperature  Curve. 

( 

\/ 

^1 

5       6        7 

H  ours 


16      17      18      19 


Discussion  of  Pycnometer  Data. 

It  is  significant  that  the  curves  for  such  a  large  variety 
of  clays  are  so  similar.  There  may  be  essential  differences 
iu  the  behavior  of  various  clays,  but  if  this  is  true,  we 
failed  to  discover  it.  The  only  difference  we  can  see  is 
that  the  non-plastic  clays  seem  to  reach  a  higher  specific 
gravity  at  950°— 1000°' C  than  do  the  plastic  clays.  An 
inspection  of  the  results  given  in  Part  2  of  this  paper  will 
also  indicate  that  this  is  true  in  general.  The  notable 
exceptions  are  in  the  case  of  Poole's  Xo.  I  China  Clay  and 
the  fire  clay  from  the  Diamond  Clay  Co.  There  is  no  doubt 
that  the  specific  gravity  of  a  burned  clay  is  the  resultant 
of  several  factors,  but  it  seems  that  the  physical  condition 
is  one  of  these. 

Lovejoy's  Settle  Curves. 

Lovejoy  (Vol.  VII,  Trans.  A.  C.  S.)  made  careful 
measurements  of  the  settle  in  brick  kilns,  from  the  time 
the  fires  were  lighted  until  the  kiln  was  finished,  and  found 
that  the  height  of  the  brick  in  the  kiln  increased  at  about 
the  temperature  of  dehydration,  indicating  an  increase  in 


6  CHEMICAL    AND   PHYSICAL    CHANGES    IN    CLAYS. 

volume  of  the  brick.  This  would  seem  to  confirm  our  re- 
sults, as  a  decrease  in  true  specific  gravity  would  give  an 
increased  volume. 

Curve  No.  3  is  one  of  the  many  which  Mr.  Love  joy 
obtained. 

TRANS     AM     CER.    SOC     VOL  XII.  KNOTE 


S3 


to 

s.4 


' 

y^ 

Wood   Drying 

Combined  Water  Staae 

[ 

\ 

\ 

Time  -S  ett Le     Curve 

\ 

For  A   BricK   Kiln  . 

See:    Trans  Am.  Cer.  Soc. Vol    W     Lovejo 

\ 

" 

\ 

I 

3 
I?  a  j/3 


Work  to  Determine  the  Causes  of  the  Specific  Gravity 
Changes  Below  1000°  C. 

It  is  evident  that  an  investigation  of  the  chemical 
properties  of  the  material  is  necessary  to  determine  the 
character  of  the  changes  indicated  by  the  specific  gravity 
determinations.  It  has  been  known  for  a  long  time  that 
weakly  ignited  clays  when  mixed  with  slaked  lime  and 
water  are  pozzuolanic  in  character  and  will  set  and  harden. 
Second,  it  has  been  pointed  out  that  dehydrated  clay  is 
much  more  soluble  in  acid  than  the  raw  material.  These 
are  the  reactions  which  were  used  to  investigate  the  char- 
acter of  dehydrated  clay. 


CHEMICAL    AND   PHYSICAL    CHANGES   IN    CLAYS.  7 

(Hay  Investigated. 

It  would  have  been  desirable  to  investigate  a  series 
of  clays,  but  since  we  could  not  do  that  a  very  pure  plastic 
fire  clay  from  Olive  Hill,  Ky.,  was  used.  It  had  about  the 
following  composition : 

Silica    47.08 

Alumina    39.86 

Oxide  of  Iron   0.88 

Lime    Tr. 

Magnesia    Tr. 

Potash    Tr. 

Soda    Tr. 

Loss  on  Ignition 12.34 

Cone  of  Fusion 34. 

This  clay  is  described  by  Greaves-Walker,  Trans.  A. 
C.  S.,  Vol.  IX. 

Behavior  with  Lime  and  Water. 
Samples  of  finely  pulverized  clay  were  ignited,  one  to 
(»00°C,  the  second  to  800° C,  a  third  to  950°C  and  another 
to  1050°C.  These  were  mixed  with  33%%  slaked  lime  by 
grinding  dry  in  a  ball  mill.  The  mixed  material  was  made 
plastic  with  water  and  moulded  into  the  regulation  tensile 
test  briquettes.  These  were  kept  in  a  damp  cellar  for 
twenty-four  hours,  and  then  immersed  in  water  for  twenty- 
eight  days.  At  the  end  of  this  time,  the  samples  which  had 
been  burned  to  600 °C  and  800° O  averaged  160  pounds  per 
square  inch,  the  950° C  sample  110  pounds  per  square  inch, 
but  the  one  which  had  been  burned  to  1050°C  slaked  down, 
giving  zero  tensile  strength.  This  shows  that  the  hydraulic 
properties  are  immediately  lessened  as  a  result  of  the 
change  which  produces  the  increase  of  specific  gravity.  To 
determine  just  how  rapidly  the  clay  loses  its  hydraulic 
properties  a  variety  of  clays  should  be  tested.  Our  work 
does  not  show  this  as  completely  as  it  should,  but  from  the 
work  we  did,  a  clay  and  lime  mixture  seems  to  behave  just 
as  a  Roman  cement,  which  is  not  surprising. 


8  CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 

Behavior  of  Dehydrated  Clay  and  Lime  Mixtures  When 
Subjected  to  High  Pressure  Steam. 

The  same  mixtures  which  were  tested  for  hydraulicity 
were  put  into  a  small  steam  cylinder,  which  was  used  for 
hardening  sand-lime  mixtures,  and  subjected  to  steam  at 
110  pounds  pressure,  for  eight  hours.  The  briquettes  made 
from  clay,  calcined  below  950°C,  gave  an  average  tensile 
strength  of  140  pounds  per  square  inch,  and  those  which 
were  heated  above  950° C  averaged  290  pounds  per  square 
inch.  The  latter  briquettes  were  much  denser  and  harder 
than  those  of  the  lower  calcined  material. 

Effects  of  Chemical  Reagents  on  Clays  Calcined  at 
Vario us  Te mp crati i res . 

The  Olive  Hill  plastic  clay  mentioned  before  was  used 
for  this  experiment  also.  Three  samples  were  used:  (1) 
raw,  (2)  calcined  to  600°C,  (3)  calcined  to  1000°C.  These 
were  boiled  four  hours  with  Na2COs  solution,  250  grams 
Na2003  per  liter,  with  very  little  effect  on  any  of  them. 
Samples  of  the  same  material  were  then  repeatedly  boiled 
with  1  :  3  HO  solution,  the  residue  being  treated  with 
dilute  alkali  solution  containing  1  gram  NaOH  and  3 
grams  Na2003  per  50  c.  c.  (See  Chemical  Examination  of 
Pozzuolane  Material,  Bulletin  3,  Geological  Survey  of 
Ohio,  Fourth  Series,  p.  111.) 

This  treatment  extracted  6%  from  the  raw  clay,  41% 
from  that  calcined  to  600°C,  and  5%  from  the  1000° C 
sample. 

This  shows  the  very  marked  difference  in  solubility 
of  the  material  calcined  at  different  temperatures.  Edgar 
ball  clay  was  tried  in  the  same  way  and  gave  about  the 
same  result,  except  70%  was  extracted  from  the  000°  O. 
sample. 

Summary  of  Results. 

(1)  When  the  chemically  combined  water  is  expelled 
from  a  clay,  compounds  are  formed  which  have  a  lower 
specific  gravity  than  the  raw  clay  itself. 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS.  9 

(2)  There  is  a  sudden  increase  in  specific  gravity 
about  950  °C,  at  which  point  Le  Chatelier  reported  an  ex- 
othermic reaction. 

(3)  Essentially  the  same  curve  was  obtained  for  all 
clays  tested. 

(4)  With  two  or  three  exceptions,  the  non-plastic 
clays  reached  slightly  higher  specific  gravity  at  950° — 
1000 'C  than  the  plastic  clays  did. 

(5)  Dehydrated  clays  which  have  not  been  heated 
above  900 °C  are  pozzuolanic  in  character,  but  lose  this 
property  rapidly  if  heated  above  950° C. 

(6)  Cmys  heated  above  950°C,  when  mixed  with 
lime  and  water  and  subjected  to  high  pressure  steam,  give 
a  very  much  stronger  body  than  similar  mixtures  of  clay 
which  were  heated  below  950° C. 

(7)  Eaw  clays  and  clays  heated  above  950°C  are  not 
attacked  appreciably  by  Na2C03,  and  but  slightly  by  HC1. 
Dehydrated  clays  heated  to  temperatures  below  900° C  are 
not  attacked  by  Na2C03,  but  are  strongly  attacked  by  HC1. 

(8)  The  residue  after  treatment  of  the  dehydrated 
clay  with  HC1  is  but  slightly  pozzuolanic  in  character. 

Conclusions. 

Our  data  does  not  show  the  water  content  of  a  clay  in 
its  various  stages  of  dehydration,  but  we  know  from  the 
work  of  others  that  the  water  does  not  all  leave  at  once, 
and  a  part  often  remains  until  the  temperature  advances 
considerably.  It  would  be  impossible  to  state  just  what  is 
formed  as  products  of  dehydration,  without  taking  this 
fact  into  consideration.  However,  we  think  we  have  evi- 
dence to  disprove  the  general  idea  that  A1203  2Si02  2H20 
breaks  down  into  Al2Os  Si02  +  Si02+2H26.  So  far  as  we 
can  find  out,  there  is  no  positive  evidence  to  support  this 
view,  but  it  is  based  on  the  fact  that  sillimanite  (A1203 
Si02)  is  stable  at  high  temperatures,  while  other  silicates 
of  alumina  are  less  so.     These  cannot  be  the  compounds 


10  CHEMICAL   AND   PHYSICAL    CHANGES   IN    CLAYS. 

really  formed  by  dehydration,  as  the  experimental  facts 
given  above  cannot  be  accounted  for  on  this  basis. 

We  wish  to  suggest  the  following  as  an  attempt  to 
explain  the  facts  noted.  A1203  2Si02  2H20  breaks  up  to 
form  A1203  Si02+Al203  3Si02+2H26  which  has  a  lower 
specific  gravity  than  the  A1203  2Si02  2H20. 

If  this  change  takes  place  in  the  clays  examined 
it  is  fairly  reasonable  to  assume  that  the  same  will  occur  in 
any  clay,  since  the  specific  gravity  changes  are  similar  in 
all  cases. 

What  causes  the  specific  gravity  to  immediately  in- 
crease after  reaching  a  minimum  we  can  not  explain,  un- 
less it  is  the  expulsion  of  the  remaining  water. 

We  have  not  proven  what  causes  the  increase 
of  specific  gravity  at  950° C,  but  hope  to  have  some  data  to 
offer  a  little  later.  It  might  be  due  either  to  the  formation 
of  an  isomeric  compound  or  to  the  combination  of  silicates 
to  produce  a  new  compound.  Either  reaction  might  evolve 
heat.  We  suggest  a  combination  of  the  above  mentioned 
silicates  to  form  A1203  2  Si02,  but  as  stated  before,  we 
have  not  proven  it.  The  behavior  of  the  clay  when  ignited 
to  1000°C,  mixed  with  lime  and  water  and  subjected  to 
high  pressure  steam,  is  a  point  against  the  formation  of  an 
isomeric  compound.  Also  numerous  writers  have  spoken 
of  AI0O0  2Si02  breaking  up  at  high  temperatures  under  the 
action  of  fluxes,  but  this  statement  may  not  be  based  on 
established  facts.  An  acid  silicate  and  a  basic  silicate  are 
known  to  be  formed  at  high  temperatures,  and  the  only 
question  is  as  to  what  breaks  up  or  changes  when  they  are 
produced. 

The  fact  that  the  non-plastic  clays  seem  to  acquire  a 
higher  specific  gravity  than  the  plastic  clays  is  probably 
due  to  the  difference  in  the  physical  condition  of  the  clays 
themselves. 


CHEMICAL    AND    PHYSICAL    CHANGES   IN    CLAYS.  11 

PART  II. 

This  part  of  the  investigation  was  devoted  to  a  study 
of  the  physical  behavior  of  typical  lire  clays  in  the  tem- 
perature interval  between  cone  010  and  cone  23.  It  was 
originally  intended  to  carry  every  clay  to  its  fusing  point, 
but  we  were  unable  to  do  this  on  account  of  an  accident  to 
the  furnace  we  were  using. 

Method  of  Procedure. 

The  nonplastic  clays  were  pulverized  to  about  8  mesh 
and  then  wet-ground  in  a  ball  mill  for  three  hours,  after 
which  all  of  them  were  plastic  enough  to  be  molded  into 
briquettes  quite  readily.  The  charge  in  the  mill  was  so 
adjusted  that  a  good  assortment  of  sizes  of  grains  was  se- 
cured, which  ran  10  mesh  and  finer.  The  plastic  clays 
were  dry-ground,  wet,  wedged,  and  molded  into  briquettes. 
The  briquettes  were  burned  in  a  coke-fired  test  kiln  to 
cone  11,  a  draw  1  icing  taken  at  the  temperatures  indicated 
on  the  following  curve  sheets.  For  temperatures  above 
cone  11,  the  oil-fired  test  kiln  described  elsewhere  in  this 
volume,  was  used. 

Duration  of  the  Heat  Treatment. 

All  the  briquettes  were  first  burned  in  the  coke-fired 
test  kiln,  the  temperature  being  raised  gradually,  cone  11 
being  reached  in  36  hours.  For  the  temperatures  above 
cone  11  the  calcined  briquettes  were  put  in  the  oil-fired 
kiln.  This  was  fired  so  as  to  reach  550°  0.  in  one  hour, 
cone  11  in  two  hours,  cone  15  in  four  hours,' cone  20  in  five 
hours,  and  cone  23  in  six  hours.  The  burns  varied  from 
this  schedule  somewhat,  but  not  enough  to  make  any  es- 
sential difference.  All  the  clays  were  carried  to  a  given 
temperature  at  the  same  time. 

Tests  After  Burning*. 

The  apparent  specific  gravity,  porosity  and  shrinkage 
of  the  briquettes  were  obtained  in  the  usual  way.  The 
followino-  curves  and  tables  show  the  results. 


12  chemical  and  physical  changes  in  clays. 

Olive  Hill,  Ky.,  Flint  Fire  Clay. 

This  clay  is  from  the  mines  of  the  Olive  Hill  Fire 
Brick  Co.  at  Olive  Hill,  Carter  County,  Kentucky.  The 
clay  deposits  of  this  region  have  been  described  by  Greaves- 
Walker,  Vol.  IX  Trans.  A.  C.  S.  The  clay  at  Olive  Hill 
is  at  the  level  of  the  Maxville  limestone,  just  at  the  top  of 
the  Sub-Carboniferous  or  Mississippian  strata. 

The  following  analysis  is  typical : 

SiO„     43.80 

ALO 40.71 

Fe2Ot     0.81 

CaO     0.96 

MgO     0.13 

Volatile    matter    13.43 

Cone  of  fusion    34-35 

Under  the  microscope  in  thin  sections,  the  clay  is 
seen  to  be  made  up  almost  entirely  of  a  structureless 
ground  mass,  which  has  very  little  effect  on  polarized  light. 
Embedded  in  the  ground  mass  are  a  very  few  rounded 
grains  of  quartz,  and  a  small  amount  of  a  micaceous  min- 
eral, a  few  grains  of  rutile,  zircon,  etc.  There  are  areas 
which  represent  pebbles  which  are  now  entirely  decom- 
posed to  a  substance  differing  from  the  material  in  which 
they  lie,  in  consequence  of  their  greater  richness  in  mica- 
ceous particles. 

RESULTS. 

The  specific  gravity  curve  proves  to  be  practically  a 
straight  line  up  to  cone  23,  which  is  a  most  unusual  condi- 
tion. Another  noteworthy  fact  is  that  the  clay  decreases  in 
porosity  between  cones  05  and  11  without  any  change  in 
specific  gravity.  The  high  fire  shrinkage  seems  to  be  char- 
acteristic of  some  flint  clays,  but  the  data  which  follows 
shows  that  it  is  not  true,  by  any  means,  of  all  of  them. 

The  microscopical  examination  failed  to  show  any 
crystalline  structure  in  this  flint  clay,  or  in  any  other  flint 
clay  examined.  Under  polarized  light,  the  ground  mass 
behaved  as  an  amorphous  substance. 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


13 


TABLE  I. 
OLIVE    HILL    FLINT   FIRE   CLAY. 
Data  Obtained  on  Burned  Briquettes. 


No. 

Heat  Treatment 

Expressed  in 

Cones 

Per  Cent                  Apparent 

Fire                       Specific 

Shrinkage                    Gravity 

Per  Cent 
Porosity 

1      

010 

05 

1 

3 

5 

7 

9 

11 

15 

20 

23 

4.0 
4.0 

6.0 
6.5 

8!6 
9.0 
9.0 
9.0 
9.5 
9.5 

2.71 
2.72 
2.69 
2.69 

2!71 
2.73 
2.74 
2.74 
2.71 
2.71 

2    

26.4 

3    

26.4 

4    

22.0 

17.8 

6    

18.0 
16.7 
14.0 
16.0 
13.5 
14.0 

8    

9    

10    

11 

T3A 

NS    ^ 

IV1.CEH.    SOC. 

/OLX 

1. 

\  NO 

re 

IC 

<b   8 
">  6 

Temperature  -  ShrinKaye  Curve 

o 

Olive  HiU,tU{.F/mt FireCiay. 

C 

*■ 

7      9 
Cones 


13       15      17       19      L\       Li     lb 


14 


CHEMICAL    AND    PHYSICAL"  CHANGES    IN    CLAYS. 


TRA 

NS. 

w    c 

ER.    . 

>OC.   V 

OL  X 

(NOTE 

■. 

L 

— < 

r-« 

. !i_ 

5 

< 

!>          ( 

> 

2.6 

■SfS 

^Z.4 

~ 

Temperature  -  Specific  Gravity  Cone. 

O/ire  Hilt,  My.  Flint  Fire  Clay. 

Z.l 

•    2.1 

010     05      I        3       5      7       9       II       13      15      17      19     21      23     25     11     Z3      31 

C  O  77  e  5 


28 
26 
24 
22 
20 
16 
16 
14 

^> 

3  I 
^> 

fc    8 

$    6 

4 


CER    SOC.    VOL) 


1    1    1    1 

1       1       1 

Tempera tt/re- Porosity  Ci/7*ve. 

Olive  Hill,  Hy.  Flint Fire -Clay. 

(S 

I 

\ 

( 

> 

o 

310     05      I        3       5      -7      9       II 
Cones 


13      15      17      19      21     23     25   .17     29     31 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


13 


Portsmouth,  O.,  Flint  Fire  Clay. 
The  geological  horizon,  occurrence,  and  properties  of 
this  clay  are  the  same  as  those  of  the  specimens  from  Olive 
Hill,  Ky.  It  is  rather  noteworthy  that,  considering  the 
great  variation  of  the  flint  clays  even  in  a  restricted  area, 
two  clays  from  such  widely  separated  deposits  should  be 
so  nearly  identical,  even  if  they  do  occur  at  the  same  hori- 
zon. 


PORTSMOUTH,  O.,  FLINT  FIRE  CLAY. 
Data  Obtained  on  Burned  Briquettes. 


No. 

Heat  Treatment 

Expressed  in 

Cones 

Per  Cent 

Fire 
Shrinkage 

Apparent 
Specific 
Gravity 

Per  Cent 
Porosity 

1      

010 
05 

1 

3 

5 

7 

9 

11 

15 

20 

23 

" 

4.48 
5.0 

7.7 
7.9 
8.0 

8!5 
9.0 
9.0 
9.0 
9.5 

2.70 
2.68 
2.71 
2.70 
2.69 

2!71 
2.72 
2.73 
2.72 
2.71 

28.0 

2    

26.3 

3    

22.1 

4    

21.0 

19.2 

6    

7    

17.6 

8    

18.0 

9    

18.0 

10    

18.0 

11    

12    

14.5 

16 


CHEMICAL    AND    PHYSICAL    CHANGES    TN    CLAYS. 


TRA, 

N5.A 

M     CE.R    SOC     VO 

XII 

KIMOTE. 

10 

_> 

«     a. 

v 

I 

<b 

Tern  per  at  are  -  Snrinftage  Curve. 

Portsmot/t/ijO.  flintfireC/czj/. 

0 

010     05      I       3        5       7       9       II       13      15      17      19     l\      23     25     27     29     31 
Co  ri  es 


TRANS. 

<\M. 

CER. 

SOC. 

VOLXII. 

KNOTE 

i 

>          , 

2.7< 

< 

> 

1 < 

r"^ 

2.6 

£f5 

**  24 

Tempera  tore  -  (Specific  Gravity  Curvt 

Portsmouth,  0,  flint  fire  Clay 

2.1 

010     OB       I       3       5       7      9       II       13      15      17      10     21      23     25     27     29     31 


CHEMICAL    AND    PHYSICAL,    CHANGES    IN    CIAYS. 


17 


.  CER    SOC.   VOL  XII. 


£'2 

Q,  10 


— ^ 

( 

t— x 

\ 

\ 

\ 

) 

Te?n/ierati/re- Porosity  Curve 

Portsmouth,  0.  Flint  Fire  day. 

13       5       7       9 
Cones 


II       13       15       17 


19     21      23     25     27    29     31 


McKeesport,  Pa.,  Flint  Fire  Clay. 

This  clay  was  supplied  by  Mr.  J.  P.  Mclntyre,  of  Mc- 
Keesport,  Pa.,  from  a  tract  in  Bell  Township,  Clearfield 
County,  Pa.  It  is  marked  MeKeesport  Clay  to  distinguish 
it  from  another  clay  also  from  Clearfield  County,  Pa. 
Nothing  is  known  of  its  exact  occurrence,  chemical  or  min- 
eral constitution.  It  was  rather  dark  in  color  and  had  the 
usual  physical  properties  of  a  flint  clay. 

RESULTS. 

The  specific  gravity  begins  to  drop  about  cone  15, 
which  distinguishes  it  from  the  Olive  Hill  and  Portsmouth 
clays.  The  porosity  and  shrinkage  seem  to  change  gradu- 
ally but  almost  continuously. 


18 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


McKEESPORT,  PA.,  FLINT  FIRE  CLAY. 
Data  Obtained  on  Burned  Briquettes. 


Heat  Treatment 
Expressed 
In  Cones 


Prr  Cent 
Fire 

Shrinkage 


Apparent 
Specific 
Gravity 


Per  Cent 
Porosity 


1 

2 
3 
4 
5 
6 
7 
8 
9 
Id 
11 


010 

05 

1 

3 

5 

7 

9 

11 

15 

20 

23 


5.3 
6.1 
6.1 
6.2 

(L8 

7!9 
8.2 
9.0 
9.5 


2.58 
2.66 
2.68 
2.65 

2.68 

2. 69 
2.70 
2.66 
2.62 


24.0 
24.0 
22.0 
21.0 

21.6 

isio 

17.8 
16.5 
15.5 


14 

TRANS.  AM.   CER.    SOC.    VOL  Kit.                                                                                                                                                                          KNOTE 

12 

10 

^>  8 

R 
£    6 

•C    4 

Temperature  -  Shrinkage    Carve. 

Me.  Hee sport,  Fa.  Flint  Fire  Ctaj/. 

2 

010     05      I       3       5      7      9       II       13      15      17     19     21      23     25     Z7     19     31 
Cones 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CI- AYS. 


19 


Tq- 

45     « 

M     C£ 

C.  VO 

L  XII- 

- 

=■ 

1 

| 

1           ,>       _ 

t 

1     * 

zt 

! 

Z.5 

' 

1 

Tcfnperature  -  SpeciYic Grav/ty  Curve 

Mc  Kees/wr£,'fa  ffint  Fire  C/au. 

Z.l 

OK      ;:       i       5       5      7      9       II       13      15     17     li1     Zl      23     -5     27    Z9     31 
Covies 


18 
26 
IM. 

TRA 

sb.  *' 

■ 

■ 

K  Is-O 

TE 

N 

- 

Vj 

20 

16 

& 

0 
klO 

6 
4 
Z 

Te  mp  e  roc  ture  -  Foroscti/  Cur  re 
Mc  Kees/iortt  Pa .  FlcntffreCiay. 

- 

010      05       I        3        5       7       9       II       13      15      17      19     21      Z^     lb     17     29     31 
Co  n  es 


20 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


Clearfield  County,  Pa.,  Flint  Fire  Clay. 

This  clay  is  being  used  at  the  present  time  for  the  man- 
ufacture of  first  class  refractory  wares.  As  nearly  as  we 
can  determine  from  survey  reports,  it  occurs  at  the  level 
of  the  Mercer  coals  in  the  Pottsville  conglomerate.  Under 
the  microscope  it  shows  a  little  more  quartz  than  the  Olive 
Hill  clay,  but  the  ground  mass  which  makes  up  the  bulk 
of  the  material  seems  to  be  the  same  and  affects  polarized 
light  very  little.  The  quartz  grains  nearly  all  exhibit 
strain  as  though  derived  from  a  schist. 

RESULTS. 

The  clay  shows  itself  to  be  of  quite  different  character 
from  the  Olive  Hill  clay.  The  specific  gravity  takes  a  de- 
cided drop  about  cone  13,  but  the  porosity  remains  un- 
changed to  a  much  higher  temperature.  The  fire  shrinkage 
is  not  high,  and  the  clay  seems  to  swell  slightly  as  the 
specific  gravity  drops.  This  is  a  condition  not  frequently 
met  with. 

CLEARFIELD  CO.,  PA.,  FLINT  FIRE  CLAY. 
Data  Obtained  on  Burned  Briquettes. 


v.. 

Heat  Treatment 
Expressed 
in  Cones 

Per  Cent 

Fire 

Shr.nkage 

Apparent 

.'peeific 

Gravity 

Per  Cent 
Porosity 

1    

010 

05 

1 

3 

5 

7 

9 

11 

15 

20 

23 

3.0 
4.3 
5.6 
5.6 

k.  6 

5'.6 
5.0 
5.0 
5.0 

2.70 
2.70 
2.68 
2.68 
.... 
2!  70 
.... 
2.70 
2.65 
2.52 
2.52 

23.0 

2    

21.0 

o 

21.0 

4    . 

21.4 

5    

6    

21.4 

8    

9    

10    

20.1 
21.0 
20.0 

11     

18.5 

CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


21 


14 

TRA 

NS.  A 

M.  CER.  SOC.  VO 

XII. 

KNOTE 

12 

Temperature  -Shrinkage  Curve. 
Clearfield  Cb,  Pa.  Flint  Fire  Clay. 

10 

8 

6 

/ 

4 

/ 

4 

/ 

I 

010     05      I       3      S      7      9       II       13      15      17      19     21      23     25     27     Z9     31 
Cones 


TR4 

vJS      A 

U.  CER.    SOC.   VOLMI 

KNOTE 

I     , 

( 

)         < 

) 

2.6 

2.5 

Sz.4 

SJZJ 

Temperature-6;ieetfLC  Gravity  Curve. 

Clearfield  Coj  Pa.  Flint  Fire  Ciaj. 

010     05       I       3       5       7      9       II       13      15 
C  ones 


19      21     23     25     17     I'd     31 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


16 
Zb 

24 

< 

TRA 

NS.  /» 

M.  CER.  SOC. 

VOLX 

■ 

<NOTE 

I 

\ 

).       ( 

)         I 

)    ■ 

ZO 

13 
16 

*' 

b 

4 

f 

) 

Temperature  -Porosity  Curye 
Clea rfietd Co,  Pa.  PlintPire  Clay. 

010       OS       I        \ 


5        7       9 
Cones 


13       15      17       19     Z\      Z3      Z5     27     Z9     31 


Savage  Mtv  Mix,  Flint  Fire  Clay. 

This  clay  occurs  at  the  same  horizon  ascribed  to  the 
Clearfield  County,  Pa.,  clay,  namely,  the  level  of  the  Mercer 
coals.  It  is  very  similar  to  the  Pennsylvania  clay,  as  the 
curves  show.  Occasional  pieces  show  a  well  marked  breccia 
structure,  with  irregular  sharp  edged  pieces  of  various 
sizes  imbedded  in  a  cementing  material,  which  must  be 
\ery  similar  in  composition  to  the  pieces  themselves. 

RESULTS. 

A  drop  in  specific  gravity  about  cone  13,  with  no 
decrease  in  porosity  accompanying  it,  but  an  increase  in 
volume  being  shown  by  the  shrinkage  measurement,  are 
the  same  features  pointed  out  in  regard  to  the  Pennsyl- 
vania clay.  This  is  the  second  case  of  flint  clays  occurring 
at  the  same  horizon,  exhibiting  about  the  same  properties, 
even  if  sejJarated  by  a  distance  of  many  miles. 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


23 


SAVAGE  MT.  FLINT  FIRE  CLAY. 
Data  Obtained  on  Burned  Briquettes. 


No. 

Heat  Treatmenet 
Kxpressed 
in  Cones 

Per  Cent                  Apparent 

Kirc                        Specific 
Shrinkage                    Gravity 

Per  Cent 
Porosity 

1     

010 
05 
1 
3 
5 
7 
9 

3.3 
3.8 

4.0 

4.8 

5.6 

2.68 
2.68 
2.68 
2.68 

2.ii 

2!  69 
2.63 
2.60 
2.53 

28.0 
28.0 
28.0 
28.0 

2 

3    

4    

K 

6    

26  0 

7    

8    

11                   5.6 
15                   4.4 
20                  3.5 
23                  2  fi 

28  0 

9    

28  0 

10    

28  0 

11    

28  0 

rRAN  j     AM.  CER    SOC.    VC 


i : 


i  o 


■5  6 

<0 


Tcm/ic 7'atu re  -  Shrinkage  Curve. 

Savage  1//.  Aid.  Flint  Fire  Clay. 

010     05       I        3       5       7      5       II       13      15      17      19      Zl      Zi     IS     27     29     31 

Cones 


24  CHEMICAL    AND    PHYSICAL    CHANGES   IN    CLAYS. 


TRA 

."■     \ 

M.  C 

ER.    SOC.    VOL  Xil 

KMOTE 

2.6 

o\ 

N- 

o 

& 

u2.i 
R 

Temperature  -  Specific  Gravity  Curve. 

<Sa  vaaeAft;  Aid.  Flint  FireClau. 

to 

2.2 

2.1 

010     OB      I        3       b       7      9        II       13      15      17      19     21      2J     25     27     26     31 
Cones 


Z8 
< 

26 
24 
22 
20 
IS 
16 

14 

*  12 
<o 

?    a 

TRA 

MS. 

o,M.   CER. 

30C. 

VOL.XII 

KNOTE 

, ,^_ 

I 

X 

( 

■> 

u 

— i 

> 

1 

Temjieratv  re  -  Porosity  Ci/rve . 

6a  vaqe  A  It,  AM .  Flint  Fire  Clay. 

^    - 

4 

OlO     05      I        3       5 
C  o  . : 


9        I!        13      15      17 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


25 


Mineral  City,  Ohio,  Flint  Fire  ("lay. 

This  clay  occurs  higher  up  in  the  geological  scale  than 
the  clays  described,  namely,  at  the  level  of  the  Lower  Kit- 
tanning  clay  and  coal.  It  shows  much  more  quartz,  when 
examined  by  the  microscope,  than  the  other  clays  do.  The 
quartz  is  characterized  by  very  sharp  edges,  which  would 
indicate  a  residual  origin. 

RESULTS. 

The  data  shows  a  drop  in  specific  gravity  at  about  the 
same  temperature  at  which  the  phenomenon  occurred  in  the 
two  preceding  clays,  but  the  porosity  begins  to  decrease 
about  cone  11.  With  the  decrease  in  porosity  also  comes 
an  increase  in  shrinkage.  This  is  the  only  flint  clay  ex- 
amined whose  physical  properties  changed,  as  we  expected 
from  a  study  of  the  plastic  clays. 

MINERAL  CITY,  O.,  FLINT  FIRE  CLAY. 
Data  Obtained  on  Burned  Briquettes. 


No. 

Heat  Treatment 
Expressed 
in  Conei 

Per  Cent 
Fire 

Shrinkafe 

Apparent 
Specific 
Gravity 

Per  Cent 
Porosity 

1      

2    

010 

05 

1 

3 

9 
11 

15 
20 
23 

2.5 
2.8 
4.3 
4.8 

5.6 

5.6 
5.6 
6.6 
7.0 

2.65 
2.67 
2.65 
2.68 
.... 
2.67 

2^68 
2.63 
2.58 
2.54 

29.0 
29.0 

3    

4    

29.0 
29.0 

6    

28.4 

1          

8    

28.0 

9    

10    

1         27.5 
25.0 

11    

|         21.0 
1 

26 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


14 

TRA 

N&.  A 

M   CER.  50C.  VO 

L  XII. 

<NO 

r£ 

12 

~^ 

Te?iiperati/re  -  <5hrir//<c\qe  Co  rye 

10 

Mineral  City,  O.  Flint  Fire  Clay. 

(3 

K 

_^ 

<0 

2 

010      05       I        3        5        7       9        II        13       15      17      10      21      23     25      17     29     31 

<?  0??  e  s 


rn/ 

NS. 

AM. 

:er. 

soc. 

VOL 

(II . 

KNOTE 

2.7 

3 - 

1 



) 

3 

2.6 

^■5 

0 

lb 
<0 

Temperature  -  Specific  Gravity  Curve. 

Mineral  City,  O.  Hint  Tire  Clay. 

ai 

010     05       I        3       5       7       9        II        13       15      17      19      21      Z3     Z5     17     23     31 
C  o  mes 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


27 


JUJ 

TRA 

N&.  A 

M     CE 

R.  SOC.  VOL  XII. 

KNOTE 

—  ^- 

• 

X 

\ 

\ 

) 

■0 

Te  m/i era ture-Poros ity  C vrve 
Mine  ra  I  City. 0.  Flint  Fire  day. 

0 

0 

/ 

010      05 


13       5       7      9 
Cones 


II       13      16      17     19     t\      15     25     17    29     Jl 


Clearfield  County,  Pa.,  Plastic  Fire  Clay. 

This  clay  is  not  a  typical  plastic  clay,  but  seems  to  be 
more  of  the  semi-flint.  It  could  be  regarded  as  one  of  the 
transition  clays  between  the  flint  and  plastic  varieties. 

RESULTS. 

Its  behavior  is  much  more  that  of  a  flint  clay  than  it 
is  of  a  plastic.  The  drop  in  porosity  is  greater  than  that 
of  any  flint  clay  examined,  but  not  as  great  as  that  of  the 
elastic  clays. 


28 


CHEMICAL   AND   PHYSICAL    CHANGES   IN    CLAYS. 


CLEARFIELD  CO.,  PA.,  PLASTIC  FIRE  CLAY. 
Data  Obtained  on  Burned  Briquettes. 


No. 

Heat  Treatment 
Expressed 
in  Cones 

Per  Cent 

Fire 
Shrinkage 

Apparent 
Specific 
Gravity 

Per  Cent 
Porosity 

1      

010 

05 
1 
3 
5 
7 
9 

11 
15 
20 
23 

2.8 
3.7 
4.9 
5.6 

Q.2 

6.2 
6.1 

6.5 

7.0 

2.66 
2.63 
2.64 
2.63 

2.64 

2l<54 
2.64 
2.58 
2.56 

26.0 

2    

22.0 

3    

21.0 

4    

21.0 

5    

6    

22.0 

7    

8    

18.0 

9    

18.0 

10    

13.0 

11    

12.0 

TRA 

N5    A 

M    CE 

R.   5C 

C    VO 

L  XII 

<NO! 

E 

12 

Temperature  -  Shrinkage  Curve. 

CLearfield.Co,Pa.  P/astic  Fire  C/aj/. 

10 

3     8 

<0 

2 

010     05       I 


•       579 
Cones 


II       13      15      17      19      21      Z3      25 


CHEMICAL   AND   PHYSICAL    CHANGES   IN    CLAYS. 


29 


TEA 

NS.  A 

v-     CER     : 

•CLXI 

\ 

(NO! 

E 

c 

V 

1 

^-~~ 

? f 

5       , 

^ 

"2 

ft  2.4 

' — 

> 

re n?//er 'at are  -  S/iectf/c  Gravity  Curve. 

Clearfield  Co,  Fa.  Plastic  Fire  Clay. 

s  • 

OIO      05       I       3       S       7      9       II       13      15      ir*  19     21      23     25     27    29     il 
Cowe5 


Z8 

TRANS-    A 

VI.  CER.    SOC.     \ 

'OL  XII. 

KNOTE 

1 

24 
Z2 

Temperature  -Porosity  Curve. 
C/ea?yietd,Pa.  P/aslFc  FireC/aj/ 

ZO 
18 
16 

SI 

«0  12 
Cb 

o10 

V 

*: 

4 
2 

OIO     05       I        3       5       7 
C  ones 


13      15      17      19      Zl      Z3      Z5     Z7     19      3\ 


80 


CHEMICAL    AND    PHYSICAL    CHANGES    IX    CLAYS. 


Olive  Hill,  Ky.,  Plastic  Fire  Clay. 

This  is  a  remarkable  plastic  clay.  It  does  not  re- 
semble any  of  the  preceding  clays  in  the  least,  so  far  as  its 
physical  properties  are  concerned,  but  it  has  very  nearly 
the  same  chemical  composition  as  the  Olive  Hill  flint  clay. 
Its  occurrence  and  properties  are  described  by  Greaves- 
Walker  in  Vol.  IX,  Trans.  A.  C.  S.,  it  being  known  locally 
as  the  Blankenship  plastic  clay.  Occurring  in  the  same 
vein  with  a  flint  clay  of  almost  identical  chemical  composi- 
tion, and  almost  the  same  cone  of  fusion,  it  serves  to  elimi- 
nate most  of  the  factors  which  have  been  suggested  to 
explain  the  difference  between  plastic  and  non-plastic 
clays. 

olive  hill,  ky.,  plastic  fire  clay. 

Data  Obtained  on  Burned  Briquettes. 


No. 

Heat  Treatment 
Expressed 
in  Cor.es 

Per  Cent 

Fire 
Shrinkage 

Apparent 

Specific 
Gravity 

Per    Cent 
Porosity 

1      

010 

05 

1 

3 

5 

7 

9 

11 

15 

20 

23 

4.1 

5.8 
7.5 
8.0 

8.0 
8.6 
9.3 
9.0 

8.8 
8.6 

2.65 
2.64 
2.64 
2.64 

2.  63 

2.56 
2.54 
2.54 

2.48 
2.44 

25.0 

2    

17.0 

3    

14.4 

4    

11.0 

5    

6    

11.0 

5.0 

8    

4.0 

9    

-3.0 

10    

2.5 

11    

2.0 

CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


31 


TP* 

N5.' 

M.  CER.   SOC.   V 

0L  111 

KMOTE 

2.7 

1 

Temperature-  Specific  Gravity  Curve 

< 

5     < 

Olive  tiM,  Ky.  P/astic  Fire  day  . 

_.G 

2.5 

-  . 

,0 

■^ 

■o 

- 


I       3       5      7      9       II       13      I 


5      r      15      ;.      23     25      27     19     31 


14 

TRA 

NS.    J 

M.    CER. 

soc. 

VOL  XII. 

KNOTE 

IZ 

Tem/ierati/re  -  Shrinkage    Carve. 

Olive  Hill,  My.  PI  as  lie  Fire  Clay. 

10 

1 

"0 

-o~ 

■ — i 

.s. 

k  1C 

0- 

2 

010     OS       I        3       5       7      9       II       13      15      17      19     Zl      23     25     27     29     31 
Cones 


32 


CHEMICAL   AND    PHYSICAL    CHANGES    IN    CLAYS. 


: 

TRA 

Ni-. 

A  IV1 .  CER. 

SOC. 

VOL  > 

» 

KINOTE 

24 
22 
20 
16 
16 
>'l4 
'  IZ 

0  io 

\ 

1 

\ 

Temperocti/re  -  Pcn^ostty   Cur*ve 
OU  ve  fie/t,  Ay.  Plastic  F/'re  Clay. 

4 
2 

010     05 


$57 
Cones 


II       13      15      \7      19      Zl      2&     25     11     16     3\ 


McKeesport,  Pa.,  Plastic  Fire  Clay. 

This  clay  is  from  the  same  locality  as  the  flint  clay 
listed  as  McKeesport,  Pa.,  flint  clay.  It  presents  nothing 
out  of  the  ordinary  except  that  in  the  raw  condition  i,t  has 
more  of  a  shale  structure  than  that  of  a  typical  fire  clay. 

McKEESPORT,   PA.,  PLASTIC  FIRE   CLAY. 
Data  Obtained  on  Burned  Briquettes. 


H  at  Treatment 
Expressed 
in  Cones 


Per   Cent 
Fire 

Shrinkage 


Apparei. t 
Specific 
Gravity 


Per  Cent 
Porosity 


1 

2 
3 
4 
5 
6 
7 
8 
9 
10 
11 


010 

3.1 

05 

3.2 

1 

3.1 

3 

4.1 

5 

7 

4.3 

9 

4.9 

11 

5.3 

15 

5.6 

20 

5.6 

23 

4.3 

2.62 

27.1 

2.64 

25.0 

2.62 

21.6 

2.62 

19.2 

2^62 

18!  7 

2.58 

15.3 

2.56 

13.4 

2.52 

11.0 

2.24 

2.0 

2.14 

2.0 

CHEMICAL   AND   PHYSICAL    CHANGES   IN    CLAYS. 


33 


14 

TR  A 

Ns. 

AM. 

CER. 

soc 

VOL 

XII. 

<NOTE 

12 

Tempera  ture-Oh rinHage     Curve. 

— 

10 

A/c  Keesport  Pa.  Plastic  Fire  Clay. 

0) 

*> 
«    8 

<;    6 

-«n 

V 

<0 

J) 

N 

i^   4 

0     ( 

y-1 

)       <j/ 

010      05       I        3       5       7       9       II       13      15      17      19      21      23     25     27     13    3\ 
C  0  )ies 


T3»Ni.  AK 

.CEH 

SOC. 

VCi  XII. 

<NO! 

1 

Tempera  ture  -  Specific  Gravity  Curve. 

Mr-   l/winn-nf   Pn   P/n.tt/'n  F/r*/?  C/rr  tf. 

c 

) 

)— <j 

rv  /\  u  i  >yi                                                                                             jy 

2.6 

b 

22,4 
8 

k 

<£ 

2.1 

) 

( 

)    Fusion 

010      05 


I        3       5       7      9       II       13      15      17      19     21      23     23     27     29     31 
Canes 


u 


CHEMTCAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


28 
26 
24 
22 

20 
18 
16 

£  12 

5,0 

^0    8 

6 

4 
2 


TRANS.    AM.   CER.    SOC.    VOL- XII 


1 

I~e)npe7%cxti/re -  Porosit  y    Curve. 
McKeespoH.Pa  P/asticpire  Clay. 

H 

, 

\ 

3-- 

1 

010      OS       I        3        5       7       3 


3      15      17      l£>     :i       23     25     27 


German  Plastic  Glass  Pot  Clay. 

Imported  clays  are  used  more  or  less  in  the  manufac- 
ture of  glass  pots,  and  as  the  clay  here  described  is  used 
for  this  purpose  its  behavior  is  of  some  interest. 

Data  Obtained  on  Burned  Briquettes. 


No. 

Heat  Treatment 
Expressed 
in  Cones 

Per  Cent 

Fire 
Shrinkage 

Apparent 

Specific 
Gravity 

Per  Cent 
Porosity 

1     

010 

05 

1 

3 

5 

7 

9 

11 

15 

20 

2.3 
2.4 
4.3 
4.3 

i'.k 

4.6 

4.6 

4.2 

Vesicular 

2.62 
2.62 
2.61 
2.60 



2.57 
2.54 
2.50 
2.21 

24.4 

2    

20.3 

3    

17.3 

4    

15.8 

5    

- 

6    

7    

8    

15.0 
7.7 
7.0 

Q 

2.0 

10      

11      

CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


35 


TRA 

NS. 

AM. 

CER 

soc 

VOL  XII. 

(NOTE . 

2.7 

Temperatue  -  Specif ic  Gravity  Co  we. 

German  Plastic   Ol ass  Pot  Ctay . 

^•5 

.°2.i 

0 

^2.2 
<0 

■~-< 

>  i/< 

'.secular 

2.1 

010      C5       I       3       5       7       9 
C  o  -n  e  5 


II       13      15      17      19 


Z7     29     31 


TRA 

NS>.    / 

M       CEH. 

=oc. 

VOL  * 

KNOTE . 

12 

10 
£    8 

7"e  mjierature  -  ShrinKaqe      Curve. 

— 

German  Plastic   Glass  Pot   Clay  . 

<*  6 

ll 

.^ 

r* 

3       '^- 

) 

--- 

--< 

)    ^esjc^/a)' 

i 

^  " 

/ 

r 

A 

0 

3       S       r       9        li       13       15      17 
Con  es 


19      21      23     25     27     29     31 


36 


CHEMICAL    AND   PHYSICAL   CHANGES   IN    CLAYS. 


28 

26 

24 

£2 

20 

18 

16 

^14 

|  It 

O|0 

J?    3 

6 

4 

2 


CER      SOC. 


Tern  pe  rent  ore  -  Porosi '  tu  C  vrve. 

German   Plastic  Glass  Pot  Clay.       , 

1 

-  — 

X 

)    Vt 

'secular 
1         i 

010     05      I        i       5       7       9       il       13      15      17      19      21      23     25     Z7     Z9     31 
Con  63 


The  foregoing  curves  show  that  there  is  a  great  differ- 
ence in  the  behavior  of  various  flint  fire  clays,  and  a  sharp 
contrast  between  the  behavior  of  flint  clays  and  plastic 
clays. 

General  Conclusions. 

We  here  present  the  specific  gravity  curves  of  a  num- 
ber of  fire  clays,  all  drawn  on  one  sheet.  The  specific  grav- 
ity below  1000°  O.  is  true  specific  gravity,  while  that  above 
that  temperature  is  apparent  specific  gravity. 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 


37 


I 


$ 

1 

o 

a1 

■: 

-9 
i 

.*! 

! 

;( 
0 

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1 
1 

> 

^ 

>5 

<5 

,<fj 

/ 

K3 

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3<S 

-/J 

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/T/uoug  ji//jji/p 


88  CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS. 

For  the  behavior  of  clays  below  1000°  0,  we  have  al- 
ready advanced  an  hypothesis,  which  is  formed  entirely  on 
experimental  data.  To  explain  the  behavior  above  cone  010, 
we  have  produced  no  experimental  data,  but  numerous  facts 
have  been  brought  out  by  others  which  help  us  to  formu- 
late an  hypothesis. 

Numerous  writers  have  pointed  oat  that  through  suffi- 
ciently severe  heating  all  clay  wares  become  more  or  less 
crystalline  in  structure.  The  clay  substance  is  said  to 
break  up  into  one  silicate  which  is  rich  in  alumina,  and 
another  rich  in  silica.  The  crystalline  substance  found  in 
porcelains  which  have  been  heated  above  1350°  C  has  been 
identified  as  sillimanite — (A1203  Si02). 

Reasoning  from  these  facts,  and  our  own  data,  we 
suggest  that  on  dehydration,  kaolinite  or  clay  substance 
breaks  down  into  two  silicates,  one  rich  in  alumina  and 
the  other  rich  in  silica.  These  silicates  are  readily  attacked 
by  reagents.  At  about  950°  C  a  pronounced  change 
takes  place,  the  exact  nature  of  which  is  still  uncertain. 
If  AloO;?  2  Si02  is  formed  at  this  temperature,  it  becomes 
unstable  as  the  temperature  advances,  and  is  decomposed 
b}^  the  action  of  fluxes,  with  the  formation  of  a  basic  and 
an  acid  silicate.  If  no  combination  of  silicates  takes  place 
at  950°  C,  but  the  change  is  due. to  the  formation  of  iso- 
meric compounds,  it  is  not  so  easy  to  explain  the  phenom- 
ena so  often  pointed  out.  Experiment  alone  can  decide 
the  question  as  to  what  really  occurs. 

The  reactions  below  cone  010  take  place  at  the  same 
temperatures  in  the  case  of  both  plastic  and  non-plastic 
clays,  since  no  constituents  are  involved  other  than  the 
clay  substance  itself.  But  above  that  temperature,  where 
other  constituents  act  on  the  clay  substance,  there  is  a 
striking  difference,  not  in  what  takes  place,  but  in  the  tem- 
perature at  which  it  takes  place.  Seger  showed  clearly 
that  this  difference  in  the  behavior  of  the  two  types  of 
clay  is  not  necessarily  due  to  difference  in  chemical  com- 
position, but  in  clays  of  similar  composition  to  a  difference 


CHEMICAL    AND    PHYSICAL    CHANGES    IN    CLAYS.  39 

in  physical  structure.  We  may  assume  then  that  the  dif- 
ference in  the  behavior  of  the  plastic  and  non-plastic  clays 
shown  above  is  primarily  due  to  this  cause. 

In  conclusion,  the  writer  wishes  to  acknowledge  his 
indebtedness  to  Mr.  R.  S.  Radcliffe  and  Mr.  A.  E^  Wil- 
liams for  valuable  assistance  in  securing  the  foregoing 
data,  and  to  Professor  C.  W.  Rolfe  for  granting-  the  use  of 
funds  and  apparatus  which  made  the  work  possible. 


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